Appreciate the input. I would say that another line at the same location isn’t a back up, that’s scaling and you can choose to run that line or not. It’s not uncommon to run a second or third line at lesser capacity than the primary line (the Nissan plant in Sunderland flex the secondary lines a lot for example).
Much of my manufacturing knowledge comes from automotive and it’s very very very rare to run a literal back up factory (as in an unused facility in a different location that’s good to go to replace another factory). They take so much man power to run, so much time to set up that it’s not economically viable to just have it on standby as a back up.
Even if you did there would be masses of business pressure to utilise the capacity.
That’s why I pointed to diversification instead, Nissan make the Qashqai in 3 locations, UK, Russia and Japan (from memory) which gives them a level of resilience but they aren’t back ups.
If Sunderland goes down then Russia and Japan plants can’t just step up and fill in.
Setting up a new factory for the DBX nearly killed Aston Martin (May still do arguably) and that was one being set up ti be used. Not sat idle waiting.